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    Subject[PATCH 23/24] tracing/kprobes: Disable kprobe events by default after creation
    Date
    From: Masami Hiramatsu <mhiramat@redhat.com>

    Disable newly created kprobe events by default, not to disturb
    another user using ftrace. "Disturb" means when someone is using
    ftrace and another user tries to use perf-tools, (in near
    future) if he defines new kprobe event via perf-tools, then new
    events will mess up the frace buffer. Fix this to allow proper
    and transparent kprobes events concurrent usage between ftrace
    users and perf users.

    Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
    Acked-by: Steven Rostedt <rostedt@goodmis.org>
    Cc: Jim Keniston <jkenisto@us.ibm.com>
    Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Frank Ch. Eigler <fche@redhat.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Jason Baron <jbaron@redhat.com>
    Cc: K.Prasad <prasad@linux.vnet.ibm.com>
    Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
    Cc: Li Zefan <lizf@cn.fujitsu.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Cc: Tom Zanussi <tzanussi@gmail.com>
    LKML-Reference: <20090914204937.18779.59422.stgit@dhcp-100-2-132.bos.redhat.com>
    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    ---
    Documentation/trace/kprobetrace.txt | 11 +++++++++--
    kernel/trace/trace_kprobe.c | 4 ++--
    2 files changed, 11 insertions(+), 4 deletions(-)

    diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
    index 6521681..9b8f7c6 100644
    --- a/Documentation/trace/kprobetrace.txt
    +++ b/Documentation/trace/kprobetrace.txt
    @@ -122,8 +122,15 @@ print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->ip, REC->dfd, R

    echo > /sys/kernel/debug/tracing/kprobe_events

    - This clears all probe points. and you can see the traced information via
    -/sys/kernel/debug/tracing/trace.
    + This clears all probe points.
    +
    + Right after definition, each event is disabled by default. For tracing these
    +events, you need to enable it.
    +
    + echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable
    + echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable
    +
    + And you can see the traced information via /sys/kernel/debug/tracing/trace.

    cat /sys/kernel/debug/tracing/trace
    # tracer: nop
    diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
    index d8db935..f6821f1 100644
    --- a/kernel/trace/trace_kprobe.c
    +++ b/kernel/trace/trace_kprobe.c
    @@ -383,7 +383,7 @@ static int register_trace_probe(struct trace_probe *tp)
    goto end;
    }

    - tp->flags = TP_FLAG_TRACE;
    + tp->rp.kp.flags |= KPROBE_FLAG_DISABLED;
    if (probe_is_return(tp))
    ret = register_kretprobe(&tp->rp);
    else
    @@ -1298,7 +1298,7 @@ static int register_probe_event(struct trace_probe *tp)
    call->id = register_ftrace_event(&tp->event);
    if (!call->id)
    return -ENODEV;
    - call->enabled = 1;
    + call->enabled = 0;
    call->regfunc = probe_event_enable;
    call->unregfunc = probe_event_disable;

    --
    1.6.2.3


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